Solid Electrolytic Capacitor for Use at High Temperatures

ABSTRACT

A capacitor that comprises a capacitor element that includes an anode that contains a dielectric formed on a sintered porous body, a solid electrolyte overlying the anode that contains manganese dioxide, and a cathode coating is provided. The cathode coating includes a barrier layer overlying the solid electrolyte and a metallization layer overlying the barrier layer. The barrier layer contains a valve metal and the metallization layer contains a metal that exhibits an electrical resistivity of about 150 nΩ·m or less (at a temperature of 20° C.) and an electric potential of about −0.5 V or more.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 62/594,609 having a filing date of Dec. 5, 2017 andU.S. Provisional Patent Application Ser. No. 62/619,159 having a filingdated of Jan. 19, 2018, which are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) are typicallymade by pressing a metal powder (e.g., tantalum) around a metal leadwire, sintering the pressed part, anodizing the sintered anode, andthereafter applying a solid electrolyte (e.g., manganese dioxide) and acathode coating that contains a carbon layer and silver resin layer. Oneproblem associated with many conventional solid electrolytic capacitors,however, is that they are relatively sensitive to high temperatures. Forexample, at temperatures of 250° C. or higher, it is believed thatcontaminant gases (e.g., carbon dioxide, carbon monoxide, etc.) can begenerated from the carbon-based binders used in the cathode coating,which are believed to have an adverse impact on electrical performance.As such, a need currently exists for a capacitor that has improvedperformance at high temperatures.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitoris disclosed that comprises a capacitor element that includes an anodethat contains a dielectric formed on a sintered porous body, a solidelectrolyte overlying the anode that contains manganese dioxide, and acathode coating. The cathode coating includes a barrier layer overlyingthe solid electrolyte and a metallization layer overlying the barrierlayer. The barrier layer contains a valve metal and the metallizationlayer contains a metal that exhibits an electrical resistivity of about150 nΩ·m or less (at a temperature of 20° C.) and an electric potentialof about −0.5 V or more.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a cross-sectional view of one embodiment of a capacitor of thepresent invention;

FIG. 2 is a cross-sectional view of another embodiment of a capacitor ofthe present invention;

FIG. 3 is a cross-sectional view of yet another embodiment of acapacitor of the present invention; and

FIG. 4 is a top view of still another embodiment of a capacitor of thepresent invention.

Repeat use of references characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor containing a capacitor element that includes ananode, solid electrolyte overlying the anode, and cathode coatingoverlying the solid electrolyte. The overall carbon content of thecapacitor element may be relatively low, such as about 2,000 parts permillion (“ppm”) or less, in some embodiments about 1,000 ppm or less,and in some embodiments, from 0 to about 500 ppm. To help achieve such alow carbon content, a variety of different aspects of the capacitorelement may be selectively controlled. For example, the solidelectrolyte and cathode coating may be formed from inorganic materials.In one embodiment, for instance, the solid electrolyte containsmanganese dioxide and the cathode coating contains one or more metallayers. For example, the cathode coating may contain a barrier layerthat overlies the solid electrolyte and a metallization that overliesthe barrier layer. The overall carbon content of the barrier layer andthe metallization layer, as well as the entire cathode coating, may berelatively low, such as about 2,000 parts per million (“ppm”) or less,in some embodiments about 1,000 ppm or less, and in some embodiments,from 0 to about 500 ppm.

By selectively controlling the nature of the solid electrolyte andcathode coating, the present inventors have discovered that theresulting capacitor may exhibit excellent electrical properties evenwhen exposed to high temperatures. For example, the capacitor may beplaced into contact with an atmosphere having a temperature of fromabout 150° C. or more, in some embodiments about 200° C. or more, and insome embodiments, from about 220° C. to about 350° C. (e.g., 250° C.).Even at such high temperatures, the capacitance may be about 30nanoFarads per square centimeter (“nF/cm²”) or more, in some embodimentsabout 100 nF/cm² or more, and in some embodiments, from about 200 toabout 30,000 nF/cm², determined at a frequency of 120 Hz. The capacitormay also exhibit a relatively low equivalence series resistance (“ESR”),such as about 500 mohms or less, in some embodiments less than about 250mohms, and in some embodiments, from about 0.1 to about 200 mohms,determined at a frequency of 100 kHz. The dissipation factor of thecapacitor may also be maintained at relatively low levels. Thedissipation factor generally refers to losses that occur in thecapacitor and is usually expressed as a percentage of the idealcapacitor performance. For example, the dissipation factor of thecapacitor of the present invention is typically from about 1% to about25%, in some embodiments from about 3% to about 10%, and in someembodiments, from about 5% to about 15%, as determined at a frequency of120 Hz. Notably, these values (e.g., capacitance, ESR, and dissipationfactor) can also remain stable at such temperatures for a substantialperiod of time, such as for about 100 hours or more, in some embodimentsfrom about 300 hours to about 3000 hours, and in some embodiments, fromabout 400 hours to about 2500 hours (e.g., about 500 hours). In oneembodiment, for example, the ratio of the capacitance value of thecapacitor after being exposed to the hot atmosphere (e.g., 230° C.) forabout 500 hours to the respective capacitance value of the capacitorwhen initially exposed to the hot atmosphere may be from about 0.7 to1.0, in some embodiments from about 0.75 to 1.0, and in someembodiments, from about 0.80 to 1.0.

Various embodiments of the capacitor will now be described in moredetail.

I. Capacitor Element

A. Anode Body

The capacitor element includes an anode that contains a dielectricformed on a sintered porous body. The porous anode body may be formedfrom a powder that contains a valve metal (i.e., metal that is capableof oxidation) or valve metal-based compound, such as tantalum, niobium,aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitridesthereof, and so forth. The powder is typically formed from a reductionprocess in which a tantalum salt (e.g., potassium fluotantalate(K₂TaF₇), sodium fluotantalate (Na₂TaF₇), tantalum pentachloride(TaCl₅), etc.) is reacted with a reducing agent. The reducing agent maybe provided in the form of a liquid, gas (e.g., hydrogen), or solid,such as a metal (e.g., sodium), metal alloy, or metal salt. In oneembodiment, for instance, a tantalum salt (e.g., TaCl₅) may be heated ata temperature of from about 900° C. to about 2,000° C., in someembodiments from about 1,000° C. to about 1,800° C., and in someembodiments, from about 1,100° C. to about 1,600° C., to form a vaporthat can be reduced in the presence of a gaseous reducing agent (e.g.,hydrogen). Additional details of such a reduction reaction may bedescribed in WO 2014/199480 to Maeshima, et al. After the reduction, theproduct may be cooled, crushed, and washed to form a powder.

The specific charge of the powder typically varies from about 2,000 toabout 800,000 microFarads*Volts per gram (“μF*V/g”) depending on thedesired application. For instance, in certain embodiments, a high chargepowder may be employed that has a specific charge of from about 100,000to about 800,000 μF*V/g, in some embodiments from about 120,000 to about700,000 μF*V/g, and in some embodiments, from about 150,000 to about600,000 μF*V/g. In other embodiments, a low charge powder may beemployed that has a specific charge of from about 2,000 to about 100,000μF*V/g, in some embodiments from about 5,000 to about 80,000 μF*V/g, andin some embodiments, from about 10,000 to about 70,000 μF*V/g. As isknown in the art, the specific charge may be determined by multiplyingcapacitance by the anodizing voltage employed, and then dividing thisproduct by the weight of the anodized electrode body.

The powder may be a free-flowing, finely divided powder that containsprimary particles. The primary particles of the powder generally have amedian size (D50) of from about 5 to about 500 nanometers, in someembodiments from about 10 to about 400 nanometers, and in someembodiments, from about 20 to about 250 nanometers, such as determinedusing a laser particle size distribution analyzer made by BECKMANCOULTER Corporation (e.g., LS-230), optionally after subjecting theparticles to an ultrasonic wave vibration of 70 seconds. The primaryparticles typically have a three-dimensional granular shape (e.g.,nodular or angular). Such particles typically have a relatively low“aspect ratio”, which is the average diameter or width of the particlesdivided by the average thickness (“D/T”). For example, the aspect ratioof the particles may be about 4 or less, in some embodiments about 3 orless, and in some embodiments, from about 1 to about 2. In addition toprimary particles, the powder may also contain other types of particles,such as secondary particles formed by aggregating (or agglomerating) theprimary particles. Such secondary particles may have a median size (D50)of from about 1 to about 500 micrometers, and in some embodiments, fromabout 10 to about 250 micrometers.

Agglomeration of the particles may occur by heating the particles and/orthrough the use of a binder. For example, agglomeration may occur at atemperature of from about 0° C. to about 40° C., in some embodimentsfrom about 5° C. to about 35° C., and in some embodiments, from about15° C. to about 30° C. Suitable binders may likewise include, forinstance, poly(vinyl butyral); poly(vinyl acetate); poly(vinyl alcohol);poly(vinyl pyrollidone); cellulosic polymers, such ascarboxymethylcellulose, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, and methylhydroxyethyl cellulose; atactic polypropylene,polyethylene; polyethylene glycol (e.g., Carbowax from Dow ChemicalCo.); polystyrene, poly(butadiene/styrene); polyamides, polyimides, andpolyacrylamides, high molecular weight polyethers; copolymers ofethylene oxide and propylene oxide; fluoropolymers, such aspolytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefincopolymers; acrylic polymers, such as sodium polyacrylate, poly(loweralkyl acrylates), poly(lower alkyl methacrylates) and copolymers oflower alkyl acrylates and methacrylates; and fatty acids and waxes, suchas stearic and other soapy fatty acids, vegetable wax, microwaxes(purified paraffins), etc.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead, which may bein the form of a wire, sheet, etc. The lead may extend in a longitudinaldirection from the anode body and may be formed from any electricallyconductive material, such as tantalum, niobium, aluminum, hafnium,titanium, etc., as well as electrically conductive oxides and/ornitrides of thereof. Connection of the lead may also be accomplishedusing other known techniques, such as by welding the lead to the body orembedding it within the anode body during formation (e.g., prior tocompaction and/or sintering).

Any binder may be removed after pressing by heating the pellet undervacuum at a certain temperature (e.g., from about 150° C. to about 500°C.) for several minutes. Alternatively, the binder may also be removedby contacting the pellet with an aqueous solution, such as described inU.S. Pat. No. 6,197,252 to Bishop, et al. Thereafter, the pellet issintered to form a porous, integral mass. The pellet is typicallysintered at a temperature of from about 700° C. to about 1600° C., insome embodiments from about 800° C. to about 1500° C., and in someembodiments, from about 900° C. to about 1200° C., for a time of fromabout 5 minutes to about 100 minutes, and in some embodiments, fromabout 8 minutes to about 15 minutes. This may occur in one or moresteps. If desired, sintering may occur in an atmosphere that limits thetransfer of oxygen atoms to the anode. For example, sintering may occurin a reducing atmosphere, such as in a vacuum, inert gas, hydrogen, etc.The reducing atmosphere may be at a pressure of from about 10 Torr toabout 2000 Torr, in some embodiments from about 100 Torr to about 1000Torr, and in some embodiments, from about 100 Torr to about 930 Torr.Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may alsobe employed.

B. Dielectric

The anode is also coated with a dielectric. The dielectric may be formedby anodically oxidizing (“anodizing”) the sintered anode so that adielectric layer is formed over and/or within the anode. For example, atantalum (Ta) anode may be anodized to tantalum pentoxide (Ta₂O₅).Typically, anodization is performed by initially applying a solution tothe anode, such as by dipping anode into the electrolyte. A solvent isgenerally employed, such as water (e.g., deionized water). To enhanceionic conductivity, a compound may be employed that is capable ofdissociating in the solvent to form ions. Examples of such compoundsinclude, for instance, acids, such as described below with respect tothe electrolyte. For example, an acid (e.g., phosphoric acid) mayconstitute from about 0.01 wt. % to about 5 wt. %, in some embodimentsfrom about 0.05 wt. % to about 0.8 wt. %, and in some embodiments, fromabout 0.1 wt. % to about 0.5 wt. % of the anodizing solution. Ifdesired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 5 toabout 200 V, and in some embodiments, from about 10 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode in that itpossesses a first portion that overlies an external surface of the anodeand a second portion that overlies an interior surface of the anode. Insuch embodiments, the first portion is selectively formed so that itsthickness is greater than that of the second portion. It should beunderstood, however, that the thickness of the dielectric layer need notbe uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process is generally employed. In each stage of the process,the sintered anode is anodically oxidized (“anodized”) to form adielectric layer (e.g., tantalum pentoxide). During the first stage ofanodization, a relatively small forming voltage is typically employed toensure that the desired dielectric thickness is achieved for the innerregion, such as forming voltages ranging from about 1 to about 90 volts,in some embodiments from about 2 to about 50 volts, and in someembodiments, from about 5 to about 20 volts. Thereafter, the sinteredbody may then be anodically oxidized in a second stage of the process toincrease the thickness of the dielectric to the desired level. This isgenerally accomplished by anodizing in an electrolyte at a highervoltage than employed during the first stage, such as at formingvoltages ranging from about 50 to about 350 volts, in some embodimentsfrom about 60 to about 300 volts, and in some embodiments, from about 70to about 200 volts. During the first and/or second stages, theelectrolyte may be kept at a temperature within the range of from about15° C. to about 95° C., in some embodiments from about 20° C. to about90° C., and in some embodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however, itis desired to employ different solutions to help better facilitate theattainment of a higher thickness at the outer portions of the dielectriclayer. For example, it may be desired that the electrolyte employed inthe second stage has a lower ionic conductivity than the electrolyteemployed in the first stage to prevent a significant amount of oxidefilm from forming on the internal surface of anode. In this regard, theelectrolyte employed during the first stage may contain an acidiccompound, such as hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage typically contains a salt of a weak acid so that thehydronium ion concentration increases in the pores as a result of chargepassage therein. Ion transport or diffusion is such that the weak acidanion moves into the pores as necessary to balance the electricalcharges. As a result, the concentration of the principal conductingspecies (hydronium ion) is reduced in the establishment of equilibriumbetween the hydronium ion, acid anion, and undissociated acid, thusforms a poorer-conducting species. The reduction in the concentration ofthe conducting species results in a relatively high voltage drop in theelectrolyte, which hinders further anodization in the interior while athicker oxide layer, is being built up on the outside to a higherformation voltage in the region of continued high conductivity. Suitableweak acid salts may include, for instance, ammonium or alkali metalsalts (e.g., sodium, potassium, etc.) of boric acid, boronic acid,acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularlysuitable salts include sodium tetraborate and ammonium pentaborate. Suchelectrolytes typically have an electrical conductivity of from about 0.1to about 20 mS/cm, in some embodiments from about 0.5 to about 10 mS/cm,and in some embodiments, from about 1 to about 5 mS/cm, determined at atemperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode may also be rinsed or washed with another solvent (e.g., water)after the first and/or second stages to remove the electrolyte.

C. Solid Electrolyte

A solid electrolyte overlies the dielectric and generally functions asthe cathode for the capacitor element. Typically, the total thickness ofthe solid electrolyte is from about 1 to about 50 μm, and in someembodiments, from about 5 to about 20 μm. In general, the solidelectrolyte includes a manganese dioxide. As is known in the art,manganese dioxide may be formed by the pyrolytic decomposition ofmanganese nitrate (Mn(NO₃)₂), such as described in U.S. Pat. No.4,945,452 to Sturmer, et al. Heating may occur, for instance, in afurnace at a temperature of from about 150° C. to about 300° C., in someembodiments from about 180° C. to about 290° C., and in someembodiments, from about 190° C. to about 260° C. Heating may beconducted in a moist or dry atmosphere. The time for the conversiondepends on the furnace temperature, heat transfer rate and atmosphere,but generally is from about 3 to about 5 minutes. After pyrolysis, theleakage current may sometimes be high due to damage suffered by thedielectric film during the deposition of the manganese dioxide. Toreduce this leakage, the capacitor may be reformed in an anodizationbath as is known in the art. For example, the capacitor may be dippedinto an electrolyte such as described above and then subjected to a DCcurrent.

D. Cathode Coating

A. Metallization Layer

As indicated, the cathode coating contains a metallization layer thatdefines an outer surface of the coating and is configured for contactwith the cathode termination. Any of a variety of known techniques maygenerally be employed to apply such a layer, such as sputtering,electrolytic plating, vapor deposition, electroless plating, etc. asdescribed in U.S. Pat. No. 4,780,797 to Libby and U.S. Pat. No.3,628,103 to Booe. Generally speaking, the metallization layer containsat least one metal that is highly conductive yet resistant to galvaniccorrosion. In this regard, the metallization layer may contain a metalthat exhibits an electrical resistivity of about 150 nanoohms-meter(“nΩ·m”) or less, in some embodiments about 100 nΩ·m or less, and insome embodiments, from 1 to about 75 nΩ·m, as determined at atemperature of 20° C. Likewise, the metal may have a relatively highelectric potential, such as about −0.5 V or more, in some embodimentsabout −0.3 V or more, and in some embodiments, from about −0.3 to about2.0 V. Particularly suitable metals for the metallization layer mayinclude, for instance, gold (resistivity of about 22 nΩ·m, electricpotential of about 1.6 V); nickel (resistivity of about 69 nΩ·m,electrical potential of about −0.2 V); silver (resistivity of about 16nΩ·m, electrical potential of about 0.8 V); tin (resistivity of about115 nΩ·m, electrical potential of about −0.1 V); copper (resistivity ofabout 17 nΩ·m, electrical potential of about 0.3 V); platinum(resistivity of about 105 nΩ·m, electric potential of about 1.2 V),iridium (resistivity of about 47 nΩ·m, electric potential of about 1.2V), palladium (resistivity of about 105 nΩ·m, electric potential ofabout 1.0 V), etc., as well as alloys thereof.

The thickness of the metallization layer may range from about 0.1 toabout 10 micrometers, in some embodiments from about 0.2 to about 5micrometers, and in some embodiments, from about 0.5 to about 1micrometer. The metallization layer may be formed from a single layercontaining one or more metals as described above. In one particularembodiment, for example, the metallization layer may be formed form asingle layer that contains nickel or an alloy thereof. Alternatively,the metallization layer may be formed from one or more sublayers, eachof which may contain one or more metals as described above. In oneparticular embodiment, for instance, the metallization layer maycontains a first sublayer that overlies the barrier layer (discussedbelow) and a second sublayer that overlies the first sublayer and definethe outer surface of the cathode coating. In such embodiments, thethickness of the second sublayer may range from about 10 nanometers toabout 1,000 nanometers, in some embodiments from about 20 nanometers toabout 500 nanometers, and in some embodiments, from about 50 nanometersto about 250 nanometers, and the thickness of the first sublayer mayrange from about 0.1 to about 10 micrometers, in some embodiments fromabout 0.2 to about 5 micrometers, and in some embodiments, from about0.5 to about 1 micrometer. While the nature of the metals within eachlayer may vary, it is typically desired that the second sublayercontains a noble metal, such as gold, silver, platinum, palladium,iridium, etc., as well as alloys thereof, and that the first sublayercontains a non-noble metal, such as tin, copper, nickel, etc., as wellas alloys thereof. Preferably, the first sublayer contains nickel or analloy thereof, and the second sublayer contains gold or an alloythereof.

B. Barrier Layer

To reduce the likelihood that the metal(s) within the metallizationlayer will diffuse into the solid electrolyte, the cathode coating mayalso contain a barrier layer that overlies the solid electrolyte and isthus positioned between the metallization layer and the solidelectrolyte. Typically, at least one valve metal is employed in thebarrier layer to enhance the ability of the layer to adhere to the solidelectrolyte. Examples of suitable valve metals may include, forinstance, tungsten, titanium, tantalum, vanadium, zinc, aluminum,molybdenum, hafnium, and zirconium, etc., as well as alloys thereof.Alloys of tungsten with one or more other valve metals are particularlysuitable for use in the barrier layer, such as alloys containingtungsten and titanium. The thickness of the barrier layer may range fromabout 0.2 to about 10 micrometers, in some embodiments from about 0.5 toabout 5 micrometers, and in some embodiments, from about 0.5 to about 2micrometers. The barrier layer may be formed from a single layercontaining one or more metals as described above. In one particularembodiment, for example, the metallization layer may be formed form asingle layer that contains a tungsten alloy. Alternatively, the barrierlayer may be formed from one or more sublayers, each of which maycontain one or more metals as described above. Regardless, any of avariety of known techniques may generally be employed to apply such alayer, such as sputtering, electrolytic plating, vapor deposition,electroless plating, etc.

II. Terminations

Once formed, the capacitor element may be provided with terminations,particularly when employed in surface mounting applications. Forexample, the capacitor may contain an anode termination to which ananode lead of the capacitor element is electrically connected and acathode termination to which the cathode of the capacitor element iselectrically connected. Any conductive material may be employed to formthe terminations, such as a conductive metal (e.g., copper, nickel,silver, nickel, zinc, tin, palladium, lead, copper, aluminum,molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof).Particularly suitable conductive metals include, for instance, copper,copper alloys (e.g., copper-zirconium, copper-magnesium, copper-zinc, orcopper-iron), nickel, and nickel alloys (e.g., nickel-iron). Thethickness of the terminations is generally selected to minimize thethickness of the capacitor. For instance, the thickness of theterminations may range from about 0.05 to about 1 millimeter, in someembodiments from about 0.05 to about 0.5 millimeters, and from about0.07 to about 0.2 millimeters. One exemplary conductive material is acopper-iron alloy metal plate available from Wieland (Germany). Ifdesired, the surface of the terminations may be electroplated withnickel, silver, gold, tin, etc. as is known in the art to ensure thatthe final part is mountable to the circuit board. In one particularembodiment, both surfaces of the terminations are plated with nickel andsilver flashes, respectively, while the mounting surface is also platedwith a tin solder layer. In yet another embodiment, the terminations maybe formed from a noble metal (e.g., gold) or have a mounting surfacethat is plated with a noble metal (e.g., gold).

The terminations may be connected to the capacitor element using anytechnique known in the art. In one embodiment, for example, a lead framemay be provided that defines the cathode termination and anodetermination. To attach the electrolytic capacitor element to the leadframe, a conductive adhesive may initially be applied to a surface ofthe cathode termination. Generally speaking, it is desirable to use anadhesive that has a relatively low organic content to minimize thepresence of carbon in the resulting capacitor element. In this regard,the conductive adhesive may employed sinterable particles that contain aconductive metal, such as copper, nickel, silver, nickel, zinc, tin,lead, copper, aluminum, molybdenum, titanium, iron, zirconium,magnesium, and alloys thereof. Silver is a particularly suitableconductive metal for use in the layer. The particles may be initiallyprovided in the form of a paste that contains metal particles of arelatively small size, such as an average size of from about 0.01 toabout 50 micrometers, in some embodiments from about 0.1 to about 40micrometers, and in some embodiments, from about 1 to about 30micrometers. Due to in part to the relatively small size of theparticles, the paste may have a relatively low viscosity, allowing it tobe readily handled and applied to an anode lead and/or anode componentduring manufacture of the capacitor. The viscosity may, for instance,range from about 5 to about 250 Pascal-seconds (Pa-s), in someembodiments from about 20 Pa-s to about 200 Pa-s, and in someembodiments, from about 30 Pa-s to about 150 Pa-s, as measured with aBrookfield DV-1 viscometer (cone and plate) operating at a speed of 5 or0.5 rpm and a temperature of 25° C. If desired, thickeners or otherviscosity modifiers may be employed in the paste to increase or decreaseviscosity. Further, the thickness of the applied paste may also berelatively thin and still achieve the desired binding of the lead to theanode component. For example, the thickness of the paste may be fromabout 0.01 to about 50 micrometers, in some embodiments from about 0.5to about 30 micrometers, and in some embodiments, from about 1 to about25 micrometers.

The metal particles used in the paste may be constituted primarily by ametal or from a composition that contains a metal as a component.Suitable metal particles may, for instance, be formed from ruthenium,rhodium, palladium, silver, osmium, iridium, platinum, gold, tantalum,niobium, aluminum, nickel, hafnium, titanium, copper, etc., as well asalloys thereof. Desirably, the metal particles are formed from a noblemetal, such as ruthenium, rhodium, palladium, silver, osmium, iridium,platinum, and gold. Silver is particularly suitable. Typically, themetal particles constitute from about 50 wt. % to about 99 wt. %, insome embodiments from about 60 wt. % to about 95 wt. %, and in someembodiments, from about 70 wt. % to about 90 wt. % of the paste.

To form the paste, the particles may be initially dispersed in asolvent. Any solvent of a variety of solvents may be employed, such aswater; glycols (e.g., propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, anddipropyleneglycol); glycol ethers (e.g., methyl glycol ether, ethylglycol ether, and isopropyl glycol ether); ethers (e.g., diethyl etherand tetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth.

In addition to the metal particles, the paste may also include otheringredients to aid in application of the layer and/or in the sinteringprocess, such as binders, sintering aids, dispersants, wetting agents,plasticizers, and so forth. For example, a sintering aid may be employedthat is a metallic compound, such as an organometallic compound,metal-organic salt, metal mercaptan, metal resinate, etc. Desirably, thesintering aid includes the same metal as the metal particles. Forinstance, when silver particles are employed, the sintering aid may be asilver mercaptan (e.g., silver t-dodecylmercaptan or silverdiethyldithiocarbamate), organosilver compound (e.g.,bis-(η1-4-phenyl-η2-1-butene)silver(I)), organic silver salt (e.g.,silver (I) hexafuoropentane-dionatecyclooctadiane complex, silverneodecanoate, silver 2,4-pentafluoropropionate, silver2,4-pentanedionate, silver tosylate, etc.), and so forth. Suitablebinders may likewise include, for instance, epoxy compounds (e.g.,two-component UHU epoxy adhesive); poly(vinyl butyral); poly(vinylacetate); poly(vinyl alcohol); poly(vinyl pyrrolidone); cellulosicpolymers, such as carboxymethylcellulose, methyl cellulose, ethylcellulose, hydroxyethyl cellulose, and methylhydroxyethyl cellulose;atactic polypropylene, polyethylene; polyethylene glycol (e.g., Carbowaxfrom Dow Chemical Co.); silicon polymers, such as poly(methyl siloxane),poly(methylphenyl siloxane); polystyrene, poly(butadiene/styrene);polyamides, polyimides, and polyacrylamides, high molecular weightpolyethers; copolymers of ethylene oxide and propylene oxide;fluoropolymers, such as polytetrafluoroethylene, polyvinylidenefluoride, and fluoro-olefin copolymers; and acrylic polymers, such assodium polyacrylate, poly(lower alkyl acrylates), poly(lower alkylmethacrylates) and copolymers of lower alkyl acrylates andmethacrylates.

Any of a variety of techniques may generally be employed to apply theconductive adhesive, such as heat treating, thermal sintering,sputtering, screen-printing, dipping, electrophoretic coating, electronbeam deposition, spraying, roller pressing, brushing, doctor bladecasting, vacuum deposition, coating, etc. Once applied, the metal pastemay be optionally dried to remove any various components, such assolvents. For instance, drying may occur at a temperature of from about20° C. to about 150° C., in some embodiments from about 50° C. to about140° C., and in some embodiments, from about 80° C. to about 130° C. Thepaste is thereafter sintered so that the particles can form a bond witheach other. The temperature at sintering occurs may vary, but istypically from about 150° C. to about 500° C., in some embodiments fromabout 180° C. to about 350° C., and in some embodiments from about 200°C. to about 300° C. Sintering may also occur at any desired pressure. Incertain embodiments, for example, sintering may occur under pressure,such as a pressure of from about 1 Megapascal (MPa) to about 50 MPa, insome embodiments from about 2 to about 30 MPa, and in some embodiments,from about 5 to about 25 MPa. The total time of sintering may varydepending on the temperature and pressure employed, but typically rangesfrom about 1 minute to about 350 minutes, in some embodiments from about50 to about 300 minutes, and in some embodiments, from about 80 minutesto about 250 minutes. The atmosphere used during sintering may alsovary. In certain embodiments, for example, sintering may occur in aninert atmosphere (e.g., nitrogen, etc.), an oxidizing atmosphere (e.g.,air or oxygen), or a reducing atmosphere (e.g., hydrogen).

The anode lead may also be electrically connected to the anodetermination using any technique known in the art, such as mechanicalwelding, laser welding, conductive adhesives, etc. Upon electricallyconnecting the anode lead to the anode termination, the conductiveadhesive may then be cured to ensure that the electrolytic capacitorelement is adequately adhered to the cathode termination.

III. Housing

Due to the ability of the capacitor to exhibit good electricalperformance at high temperatures, it is not necessary for the capacitorelement to be hermetically sealed within a housing. Nevertheless, incertain embodiments, it may be desired to hermetically seal thecapacitor element within a housing. In one embodiment, for example, thecapacitor element may be hermetically sealed within a housing in thepresence of a gaseous atmosphere that contains an inert gas.

The capacitor element may be sealed within a housing in various ways. Incertain embodiments, for instance, the capacitor element may be enclosedwithin a case, which may then be filled with a resinous material, suchas a thermoset resin (e.g., epoxy resin) that can be cured to form ahardened housing. Examples of such resins include, for instance, epoxyresins, polyimide resins, melamine resins, urea-formaldehyde resins,polyurethane resins, phenolic resins, polyester resins, etc. Epoxyresins are also particularly suitable. Still other additives may also beemployed, such as photoinitiators, viscosity modifiers, suspensionaiding agents, pigments, stress reducing agents, non-conductive fillers,stabilizers, etc. For example, the non-conductive fillers may includeinorganic oxide particles, such as silica, alumina, zirconia, magnesiumoxide, iron oxide, copper oxide, zeolites, silicates, clays (e.g.,smectite clay), etc., as well as composites (e.g., alumina-coated silicaparticles) and mixtures thereof. Regardless, the resinous material maysurround and encapsulate the capacitor element so that at least aportion of the anode and cathode terminations are exposed for mountingonto a circuit board. When encapsulated in this manner, the capacitorelement and resinous material form an integral capacitor.

Of course, in alternative embodiments, it may be desirable to enclosethe capacitor element within a housing that remains separate anddistinct. In this manner, the atmosphere of the housing can possess acertain degree of moisture such that it is considered a humidatmosphere. For example, the relative humidity of the atmosphere may beabout 40% or more, in some embodiments about 45% or more, and in someembodiments, from about 50% to about 95% (e.g., about 50%). Inalternative embodiments, however, the atmosphere may be relatively dryso that it has a relative humidity of less than about 40%, in someembodiments about 30% or less, in some embodiments about 10% or less,and in some embodiments, from about 0.001 to about 5%. For example, theatmosphere may be gaseous and contain at least one inert gas, such asnitrogen, helium, argon, xenon, neon, krypton, radon, and so forth, aswell as mixtures thereof. Typically, inert gases constitute the majorityof the atmosphere within the housing, such as from about 50 wt. % to 100wt. %, in some embodiments from about 75 wt. % to 100 wt. %, and in someembodiments, from about 90 wt. % to about 99 wt. % of the atmosphere. Ifdesired, a relatively small amount of non-inert gases may also beemployed, such as carbon dioxide, oxygen, water vapor, etc. In suchcases, however, the non-inert gases typically constitute 15 wt. % orless, in some embodiments 10 wt. % or less, in some embodiments about 5wt. % or less, in some embodiments about 1 wt. % or less, and in someembodiments, from about 0.01 wt. % to about 1 wt. % of the atmospherewithin the housing.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof.

The housing may have any desired shape, such as cylindrical, D-shaped,rectangular, triangular, prismatic, etc. Referring to FIG. 1, forexample, one embodiment of a capacitor 100 is shown that contains ahousing 122 and a capacitor element 120. In this particular embodiment,the housing 122 is generally rectangular. Typically, the housing and thecapacitor element have the same or similar shape so that the capacitorelement can be readily accommodated within the interior cavity. In theillustrated embodiment, for example, both the capacitor element 120 andthe housing 122 have a generally rectangular shape.

If desired, the capacitor of the present invention may exhibit arelatively high volumetric efficiency. To facilitate such highefficiency, the capacitor element typically occupies a substantialportion of the volume of an interior cavity of the housing. For example,the capacitor element may occupy about 30 vol. % or more, in someembodiments about 50 vol. % or more, in some embodiments about 60 vol. %or more, in some embodiments about 70 vol. % or more, in someembodiments from about 80 vol. % to about 98 vol. %, and in someembodiments, from about 85 vol. % to 97 vol. % of the interior cavity ofthe housing. To this end, the difference between the dimensions of thecapacitor element and those of the interior cavity defined by thehousing are typically relatively small.

Referring to FIG. 1, for example, the capacitor element 120 may have alength (excluding the length of the anode lead 6) that is relativelysimilar to the length of an interior cavity 126 defined by the housing122. For example, the ratio of the length of the anode to the length ofthe interior cavity ranges from about 0.40 to 1.00, in some embodimentsfrom about 0.50 to about 0.99, in some embodiments from about 0.60 toabout 0.99, and in some embodiments, from about 0.70 to about 0.98. Thecapacitor element 120 may have a length of from about 5 to about 10millimeters, and the interior cavity 126 may have a length of from about6 to about 15 millimeters. Similarly, the ratio of the height of thecapacitor element 120 (in the −z direction) to the height of theinterior cavity 126 may range from about 0.40 to 1.00, in someembodiments from about 0.50 to about 0.99, in some embodiments fromabout 0.60 to about 0.99, and in some embodiments, from about 0.70 toabout 0.98. The ratio of the width of the capacitor element 120 (in the−x direction) to the width of the interior cavity 126 may also rangefrom about 0.50 to 1.00, in some embodiments from about 0.60 to about0.99, in some embodiments from about 0.70 to about 0.99, in someembodiments from about 0.80 to about 0.98, and in some embodiments, fromabout 0.85 to about 0.95. For example, the width of the capacitorelement 120 may be from about 2 to about 7 millimeters and the width ofthe interior cavity 126 may be from about 3 to about 10 millimeters, andthe height of the capacitor element 120 may be from about 0.5 to about 2millimeters and the width of the interior cavity 126 may be from about0.7 to about 6 millimeters.

Although by no means required, the capacitor element may be attached tothe housing in such a manner that an anode termination and cathodetermination are formed external to the housing for subsequentintegration into a circuit. The particular configuration of theterminations may depend on the intended application. In one embodiment,for example, the capacitor may be formed so that it is surfacemountable, and yet still mechanically robust. For example, the anodelead may be electrically connected to external, surface mountable anodeand cathode terminations (e.g., pads, sheets, plates, frames, etc.).Such terminations may extend through the housing to connect with thecapacitor.

Although by no means required, connective members may optionally beemployed within the interior cavity of the housing to facilitateconnection to the terminations in a mechanically stable manner. Forexample, referring again to FIG. 1, the capacitor 100 may include aconnection member 162 that is formed from a first portion 167 and asecond portion 165. The connection member 162 may be formed fromconductive materials similar to the external terminations. The firstportion 167 and second portion 165 may be integral or separate piecesthat are connected together, either directly or via an additionalconductive element (e.g., metal). In the illustrated embodiment, thesecond portion 165 is provided in a plane that is generally parallel toa lateral direction in which the lead 6 extends (e.g., −y direction).The first portion 167 is “upstanding” in the sense that it is providedin a plane that is generally perpendicular the lateral direction inwhich the lead 6 extends. In this manner, the first portion 167 canlimit movement of the lead 6 in the horizontal direction to enhancesurface contact and mechanical stability during use. If desired, aninsulative material 7 (e.g., Teflon™ washer) may be employed around thelead 6.

The first portion 167 may possess a mounting region (not shown) that isconnected to the anode lead 6. The region may have a “U-shape” forfurther enhancing surface contact and mechanical stability of the lead6. Connection of the region to the lead 6 may be accomplished using anyof a variety of known techniques, such as welding, laser welding,conductive adhesives, etc. In one particular embodiment, for example,the region is laser welded to the anode lead 6. Regardless of thetechnique chosen, however, the first portion 167 can hold the anode lead6 in substantial horizontal alignment to further enhance the dimensionalstability of the capacitor 100.

Referring again to FIG. 1, one embodiment of the present invention isshown in which the optional connective member 162 and capacitor element120 are connected to the housing 122 through anode and cathodeterminations 127 and 129, respectively. More specifically, the housing122 of this embodiment includes an outer wall 123 and two opposingsidewalls 124 between which a cavity 126 is formed that includes thecapacitor element 120. The outer wall 123 and sidewalls 124 may beformed from one or more layers of a metal, plastic, or ceramic materialsuch as described above. In this particular embodiment, the anodetermination 127 contains a first region 127 a that is positioned withinthe housing 122 and electrically connected to the connection member 162and a second region 127 b that is positioned external to the housing 122and provides a mounting surface 201. Likewise, the cathode termination129 contains a first region 129 a that is positioned within the housing122 and electrically connected to the solid electrolyte of the capacitorelement 120 and a second region 129 b that is positioned external to thehousing 122 and provides a mounting surface 203. It should be understoodthat the entire portion of such regions need not be positioned within orexternal to the housing.

In the illustrated embodiment, a conductive trace 127 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. Similarly, a conductive trace 129 c extends in theouter wall 123 of the housing to connect the first region 127 a andsecond region 127 b. The conductive traces and/or regions of theterminations may be separate or integral. In addition to extendingthrough the outer wall of the housing, the traces may also be positionedat other locations, such as external to the outer wall. Of course, thepresent invention is by no means limited to the use of conductive tracesfor forming the desired terminations.

Regardless of the particular configuration employed, connection of theterminations 127 and 129 to the capacitor element 120 may be made usingany known technique, such as welding, laser welding, conductiveadhesives, etc. In one particular embodiment, for example, a conductiveadhesive 131 is used to connect the second portion 165 of the connectionmember 162 to the anode termination 127. Likewise, a conductive adhesive133 is used to connect the cathode of the capacitor element 120 to thecathode termination 129.

Optionally, a polymeric restraint may also be disposed in contact withone or more surfaces of the capacitor element, such as the rear surface,front surface, upper surface, lower surface, side surface(s), or anycombination thereof. The polymeric restraint can reduce the likelihoodof delamination by the capacitor element from the housing. In thisregard, the polymeric restraint may possesses a certain degree ofstrength that allows it to retain the capacitor element in a relativelyfixed positioned even when it is subjected to vibrational forces, yet isnot so strong that it cracks. For example, the restraint may possess atensile strength of from about 1 to about 150 MPa, in some embodimentsfrom about 2 to about 100 MPa, in some embodiments from about 10 toabout 80 MPa, and in some embodiments, from about 20 to about 70 MPa,measured at a temperature of about 25° C. It is normally desired thatthe restraint is not electrically conductive. Referring again to FIG. 1,for instance, one embodiment is shown in which a single polymericrestraint 197 is disposed in contact with an upper surface 181 and rearsurface 177 of the capacitor element 120. While a single restraint isshown in FIG. 1, it should be understood that separate restraints may beemployed to accomplish the same function. In fact, more generally, anynumber of polymeric restraints may be employed to contact any desiredsurface of the capacitor element. When multiple restraints are employed,they may be in contact with each other or remain physically separated.For example, in one embodiment, a second polymeric restraint (not shown)may be employed that contacts the upper surface 181 and front surface179 of the capacitor element 120. The first polymeric restraint 197 andthe second polymeric restraint (not shown) may or may not be in contactwith each other. In yet another embodiment, a polymeric restraint mayalso contact a lower surface 183 and/or side surface(s) of the capacitorelement 120, either in conjunction with or in lieu of other surfaces.

Regardless of how it is applied, it is typically desired that thepolymeric restraint is also in contact with at least one surface of thehousing to help further mechanically stabilize the capacitor elementagainst possible delamination. For example, the restraint may be incontact with an interior surface of one or more sidewall(s), outer wall,lid, etc. In FIG. 1, for example, the polymeric restraint 197 is incontact with an interior surface 107 of sidewall 124 and an interiorsurface 109 of outer wall 123. While in contact with the housing, it isnevertheless desired that at least a portion of the cavity defined bythe housing remains unoccupied to allow for the inert gas to flowthrough the cavity and limit contact of the solid electrolyte withoxygen. For example, at least about 5% of the cavity volume typicallyremains unoccupied by the capacitor element and polymer restraint, andin some embodiments, from about 10% to about 50% of the cavity volume.

Once connected in the desired manner, the resulting package ishermetically sealed as described above. Referring again to FIG. 1, forinstance, the housing 122 may also include a lid 125 that is placed onan upper surface of side walls 124 after the capacitor element 120 andthe polymer restraint 197 are positioned within the housing 122. The lid125 may be formed from a ceramic, metal (e.g., iron, copper, nickel,cobalt, etc., as well as alloys thereof), plastic, and so forth. Ifdesired, a sealing member 187 may be disposed between the lid 125 andthe side walls 124 to help provide a good seal. In one embodiment, forexample, the sealing member may include a glass-to-metal seal, Kovar®ring (Goodfellow Camridge, Ltd.), etc. The height of the side walls 124is generally such that the lid 125 does not contact any surface of thecapacitor element 120 so that it is not contaminated. The polymericrestraint 197 may or may not contact the lid 125. When placed in thedesired position, the lid 125 is hermetically sealed to the sidewalls124 using known techniques, such as welding (e.g., resistance welding,laser welding, etc.), soldering, etc. Hermetic sealing generally occursin the presence of inert gases as described above so that the resultingcapacitor is substantially free of reactive gases, such as oxygen.

It should be understood that the embodiments described are onlyexemplary, and that various other configurations may be employed in thepresent invention for hermetically sealing a capacitor element within ahousing. Referring to FIG. 2, for instance, another embodiment of acapacitor 200 is shown that employs a housing 222 that includes an outerwall 123 and a lid 225 between which a cavity 126 is formed thatincludes the capacitor element 120 and polymeric restraint 197. The lid225 includes an outer wall 223 that is integral with at least onesidewall 224. In the illustrated embodiment, for example, two opposingsidewalls 224 are shown in cross-section. The outer walls 223 and 123both extend in a lateral direction (−y direction) and are generallyparallel with each other and to the lateral direction of the anode lead6. The sidewall 224 extends from the outer wall 223 in a longitudinaldirection that is generally perpendicular to the outer wall 123. Adistal end 500 of the lid 225 is defined by the outer wall 223 and aproximal end 501 is defined by a lip 253 of the sidewall 224.

The lip 253 extends from the sidewall 224 in the lateral direction,which may be generally parallel to the lateral direction of the outerwall 123. The angle between the sidewall 224 and the lip 253 may vary,but is typically from about 60° to about 120°, in some embodiments fromabout 70° to about 110°, and in some embodiments, from about 80° toabout 100° (e.g., about 90°). The lip 253 also defines a peripheral edge251, which may be generally perpendicular to the lateral direction inwhich the lip 253 and outer wall 123 extend. The peripheral edge 251 islocated beyond the outer periphery of the sidewall 224 and may begenerally coplanar with an edge 151 of the outer wall 123. The lip 253may be sealed to the outer wall 123 using any known technique, such aswelding (e.g., resistance or laser), soldering, glue, etc. For example,in the illustrated embodiment, a sealing member 287 is employed (e.g.,glass-to-metal seal, Kovar® ring, etc.) between the components tofacilitate their attachment. Regardless, the use of a lip describedabove can enable a more stable connection between the components andimprove the seal and mechanical stability of the capacitor.

Still other possible housing configurations may be employed in thepresent invention. For example, FIG. 3 shows a capacitor 300 having ahousing configuration similar to that of FIG. 2, except that terminalpins 327 b and 329 b are employed as the external terminations for theanode and cathode, respectively. More particularly, the terminal pin 327a extends through a trace 327 c formed in the outer wall 323 and isconnected to the anode lead 6 using known techniques (e.g., welding). Anadditional section 327 a may be employed to secure the pin 327 b.Likewise, the terminal pin 329 b extends through a trace 329 c formed inthe outer wall 323 and is connected to the cathode via a conductiveadhesive 133 as described above.

The embodiments shown in FIGS. 1-3 are discussed herein in terms of onlya single capacitor element. It should also be understood, however, thatmultiple capacitor elements may also be hermetically sealed within ahousing. The multiple capacitor elements may be attached to the housingusing any of a variety of different techniques. Referring to FIG. 4, forexample one particular embodiment of a capacitor 400 that contains twocapacitor elements is shown and will now be described in more detail.More particularly, the capacitor 400 includes a first capacitor element420 a in electrical communication with a second capacitor element 420 b.In this embodiment, the capacitor elements are aligned so that theirmajor surfaces are in a horizontal configuration. That is, a majorsurface of the capacitor element 420 a defined by its width (−xdirection) and length (−y direction) is positioned adjacent to acorresponding major surface of the capacitor element 420 b. Thus, themajor surfaces are generally coplanar. Alternatively, the capacitorelements may be arranged so that their major surfaces are not coplanar,but perpendicular to each other in a certain direction, such as the −zdirection or the −x direction. Of course, the capacitor elements neednot extend in the same direction.

The capacitor elements 420 a and 420 b are positioned within a housing422 that contains an outer wall 423 and sidewalls 424 and 425 thattogether define a cavity 426. Although not shown, a lid may be employedthat covers the upper surfaces of the sidewalls 424 and 425 and sealsthe capacitor 400 as described above. Optionally, a polymeric restraintmay also be employed to help limit the vibration of the capacitorelements. In FIG. 4, for example, separate polymer restraints 497 a and497 b are positioned adjacent to and in contact with the capacitorelements 420 a and 420 b, respectively. The polymer restraints 497 a and497 b may be positioned in a variety of different locations. Further,one of the restraints may be eliminated, or additional restraints may beemployed. In certain embodiments, for example, it may be desired toemploy a polymeric restraint between the capacitor elements to furtherimprove mechanical stability.

In addition to the capacitor elements, the capacitor also contains ananode termination to which anode leads of respective capacitor elementsare electrically connected and a cathode termination to which thecathodes of respective capacitor elements are electrically connected.Referring again to FIG. 4, for example, the capacitor elements are shownconnected in parallel to a common cathode termination 429. In thisparticular embodiment, the cathode termination 429 is initially providedin a plane that is generally parallel to the bottom surface of thecapacitor elements and may be in electrical contact with conductivetraces (not shown). The capacitor 400 also includes connective members427 and 527 that are connected to anode leads 407 a and 407 b,respectively, of the capacitor elements 420 a and 420 b. Moreparticularly, the connective member 427 contains an upstanding portion465 and a planar portion 463 that is in connection with an anodetermination (not shown). Likewise, the connective 527 contains anupstanding portion 565 and a planar portion 563 that is in connectionwith an anode termination (not shown). Of course, it should beunderstood that a wide variety of other types of connection mechanismsmay also be employed.

The present invention may be better understood by reference to thefollowing examples.

Test Procedures Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using a Keithley 3330Precision LCZ meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency may 100 kHz andthe temperature may be 23° C.±2° C.

Capacitance (CAP)

The capacitance may be measured using a Keithley 3330 Precision LCZmeter with Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak topeak sinusoidal signal. The operating frequency may be 120 Hz and thetemperature may be 23° C.±2° C.

Temperature Life Testing

The capacitors have been stored under life conditions 250° C./0.5 Ur andtested for electrical performance (ESR and CAP tests conducted at 23°C.±2° C.).

Example 1

A tantalum anode (5.35 mm×3.70 mm×1.00 mm) was anodized at 115V in aliquid electrolyte to 10 μF. A conductive coating was then formed bydipping the entire anode into an aqueous solution of manganese(II)nitrate and then decomposed at 250° C. The part was coated withtitanium-tungsten alloy barrier layer followed by nickel and goldmetallization layers using Baltec sputter coater. A copper-basedleadframe material was used to finish the assembly process. The tantalumwire of the capacitor element was then laser welded to an anodeconnective member. The cathode connective member was then glued with thesilver adhesive to a gold cathode termination and the anode connectivemember was then welded to a gold anode termination located inside aceramic housing having a length of 11.00 mm, a width of 6.00 mm, and athickness of 2.20 mm. The adhesive for the connections was a paste thatcontains sintered silver particles (Loctite SSP2020). The adhesive wasapplied between cathode connective member and gold-plated solder pad andwas dried at 250° C. for 60 minutes. The resulting assembly was placedinto a welding chamber and purged with nitrogen gas before seam weldingbetween the seal ring and the lid was performed. Multiple parts (20) of10 μF/35V rated capacitors in ceramic case were made in this manner.

Example 2

Capacitors were formed in the manner described in Example 1, except thatthe part was coated with graphite and silver instead of barrier andmetallization layers. Multiple parts (20) of 10 μF/35V rated capacitorsin ceramic case were made in this manner.

The finished capacitors of Examples were then tested for electricalperformance under life conditions 250° C./0.5 Ur. The median results ofCAP and ESR are set forth below in Table 1. The fails represented partswith CAP drop more than 50%.

TABLE 1 Electrical Properties Cap ESR fails [μF] [mohms] [%] 0 h 500 h1000 h 0 h 500 h 1000 h 0 h 500 h 1000 h Example 1 10.67 10.51 10.46 159214 286 0 0 0 Example 2 11.35 11.12 11.11 89 128 188 0 0 80

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A capacitor comprising a capacitor element thatincludes: an anode that contains a dielectric formed on a sinteredporous body; a solid electrolyte overlying the anode that containsmanganese dioxide; and a cathode coating that includes: a barrier layeroverlying the solid electrolyte, wherein the barrier layer contains avalve metal; and a metallization layer overlying the barrier layer,wherein the metallization layer contains a metal that exhibits anelectrical resistivity of about 150 nΩ·m or less (at a temperature of20° C.) and an electric potential of about −0.5 V or more.
 2. Thecapacitor of claim 1, wherein the metallization layer includes gold,nickel, silver, tin, copper, platinum, iridium, palladium, or an alloythereof.
 3. The capacitor of claim 1, wherein the metallization layerhas a thickness of from about 0.1 to about 10 micrometers.
 4. Thecapacitor of claim 1, wherein the metallization layer is formed from asingle layer.
 5. The capacitor of claim 4, wherein the single layerincludes nickel or an alloy thereof.
 6. The capacitor of claim 1,wherein the metallization layer contains a first sublayer that overliesthe barrier layer and a second sublayer that overlies the firstsublayer.
 7. The capacitor of claim 6, wherein the second sublayercontains a noble metal.
 8. The capacitor of claim 7, wherein the noblemetal is gold or an alloy thereof.
 9. The capacitor of claim 6, whereinthe first sublayer contains nickel or an alloy thereof.
 10. Thecapacitor of claim 1, wherein the valve metal of the barrier layerincludes tungsten, titanium, tantalum, vanadium, zinc, aluminum,molybdenum, hafnium, and zirconium, or an alloy thereof.
 11. Thecapacitor of claim 10, wherein the valve metal of the barrier layerincludes an alloy of tungsten.
 12. The capacitor of claim 1, wherein thecapacitor element has a carbon content of about 2,000 ppm or less. 13.The capacitor of claim 1, wherein the cathode coating has a carboncontent of about 2,000 ppm or less.
 14. The capacitor of claim 1,further comprising: an anode termination in electrical contact with theanode; and a cathode termination in electrical contact with the cathodecoating.
 15. The capacitor of claim 14, wherein a conductive adhesiveelectrically connects the cathode termination to the cathode coating.16. The capacitor of claim 15, wherein the conductive adhesive includessinterable metal particles.
 17. The capacitor of claim 16, wherein themetal particles include silver.
 18. The capacitor of claim 1, whereinthe anode body includes tantalum.
 19. The capacitor of claim 1, whereinthe capacitor exhibits a capacitance of about 30 nanoFarads per squarecentimeter or more, an equivalence series resistance of about 500 mohmsor less, and/or a dissipation factor of from about 1% to about 25%. 20.The capacitor of claim 19, wherein the capacitor exhibits a capacitanceof about 30 nanoFarads per square centimeter or more, an equivalenceseries resistance of about 500 mohms or less, and/or a dissipationfactor of from about 1% to about 25%, after being exposed to atemperature of 250° C. for about 500 hours.
 21. The capacitor of claim1, further comprising a housing within which the capacitor element isenclosed.
 22. The capacitor of claim 21, wherein the housing is formedfrom a resinous material that encapsulates the capacitor element. 23.The capacitor of claim 21, wherein the housing defines an interiorcavity within which the capacitor element is positioned, wherein theinterior cavity has a gaseous atmosphere.
 24. The capacitor of claim 23,wherein the gaseous atmosphere contains an inert gas.